Videos: Worst rainforest fires in history in Brazil.

It came, witnesses said, quickly and without warning. One compared it to the “apocalypse”.

Sao Paulo – the largest city in the Americas – was plunged into afternoon darkness after vast plumes of smoke from forest fires burning across the continent suddenly swept over the city.

Brazilians living in the coastal metropolis saw day turned to night for more than an hour from 3 pm on Monday.

Pictures posted to social media by alarmed residents – many unsure what was happening – show the city in the near pitch black. “The final judgment is coming,” one person noted on Twitter.

Experts have indicated the phenomenon was at least partially caused by the oft-deliberate burning of South America’s vast swathes of forests to make way for farmland.

“The smoke [came] from very dense and wide fires that have been happening for several days in [the state of] Rondonia and Bolivia,” Josélia Pegorim, a meteorologist with Climatempo, told the Globo TV network.

The blackout came on the same day new figures showed Brazil’s Amazon rainforest has seen a record number of fires this year.

The country’s National Institute for Space Research (Inpe) said it had detected more than 72,000 blazes between January and August – the highest number since records began in 2013. The figure is an 83 percent increase in the same period in 2018.

Although it is not unusual for such wildfires to occur in Brazil’s dry season, experts believe an increasing number are being deliberately started in efforts to illegally deforest land for settlement and cattle ranching.

“The dry season creates the favorable conditions for the use and spread of fire, but starting a fire is the work of humans, either deliberately or by accident,” Alberto Setzer, a researcher with Inpe, said.

Footage posted on social media purported to show forest fires raging alongside a road in Brazil.

The fate of the Amazon is widely considered by climate change experts as key to the future of the planet, with the rainforest providing more than 20 percent of the planet’s oxygen.

Because it is the world’s largest rainforest, it is a vital carbon store that slows down global warming. Its destruction – deliberate or otherwise – reduces the ability of nature to suck carbon from the atmosphere.

Yet Brazil’s far-right president Jair Bolsonaro, who came into power promising to clear vast tracts of the rainforest for development, remains unmoved.

Just last week, ahead of the new figures being released, he sacked the head of Inpe amid rows over its deforestation data. He called the figures “lies”.

Speaking to Reuters afterward, he dismissed concerns about the rainforest’s destruction by saying farmers needed land.

“I used to be called Captain Chainsaw,” he said. “Now I am Nero, setting the Amazon aflame.”